The use of catalysts for the oxidation of carbon monoxide to carbon dioxide by reaction with oxygen, particularly at low temperature, is of much interest in, for example, breathing masks designed for removing carbon monoxide from inhaled air and carbon dioxide lasers for combining carbon monoxide and oxygen formed by dissociation of carbon dioxide during discharge. However, known carbon monoxide oxidation catalysts are generally air-sensitive. That is, the catalysts partially deactivate on exposure to atmospheric air. Therefore, there is an ever present need to develop a new carbon monoxide catalyst composition and a process for producing the composition.